Rechargeable or secondary lithium batteries are often used in electronic devices requiring a steady and reliable source of electrical energy. The essential components of a rechargeable lithium battery are an anode or negative electrode, a cathode or positive electrode and a lithium ion conducting non-aqueous electrolyte. The anode active component of a rechargeable lithium battery is a substance which is capable of inserting or intercalating lithium ions when the battery is charged and releasing lithium ions when the battery is discharged. The cathode active component of a rechargeable lithium battery is capable of incorporating lithium ions reversibly, whereby the lithium ions are released when the battery is charged and are reincorporated in the cathode active component on discharge. The electrolyte of a rechargeable lithium battery is usually a non-aqueous electrolyte, most commonly a solid or liquid polymer bearing a lithium compound having dissociable lithium ions, or a microporous polymer which has been impregnated with an organic liquid having a lithium salt dissolved therein, or any non-aqueous substance that is capable of conducting electricity by means of movement of lithium ions. The cathode active component is commonly a lithium containing chalcogenide, most frequently a lithium containing transition metal oxide.
Transition metal oxides and solid solutions of such oxides have been known to be utilized in the positive electrode of a rechargeable lithium battery and are described, for example, in U.S. Pat. No. 5,518,842, issued on May 21, 1996 to Fey et al.
Carbon in the form of graphite or petroleum coke or similar high purity carbon particles, which readily intercalates lithium ions, is often used as the anode active substance in rechargeable lithium batteries. It is known that a portion of the lithium inserted in the carbon particles and similar intercalating substances, is retained irreversibly, the irreversibility may be affected by several factors, such as history of the heat treatment of the carbon particles, variations in crystal structure, particle size and so on, resulting in different amounts of irreversibly retained lithium in the anode. The reversible capacity of carbon in a lithium ion battery varies between 310 and 380 mAh/g (443.4-533.4 mAh/cm.sup.3, based on 1.43 g/cm.sup.3 bulk density for graphite commonly used in carbon anodes). Carbon in the form utilized in anodes, is relatively inexpensive and readily available, however, the energy density that carbon containing anodes are capable of providing is usually not as high as would be desirable; furthermore, carbon is light and voluminous, hence cannot be packed densely, which further reduces the energy density obtainable from negative electrodes containing carbon as the anode active substance. It is to be noted, however, that most rechargeable lithium batteries contain some lithium which does not participate in the charging-discharging process step in other battery components, that is usually the cathode and the electrolyte also have a portion of irreversibly bonded lithium ions.
There are publications describing substances other than carbon, which are capable of reversibly inserting lithium ions. U.S. Pat. No. 5,294,503, issued on Mar. 15, 1994, to Chen-Kuo Huang et al. teaches the utilization of lithium-magnesium-silicon compounds as anodes in a rechargeable lithium battery. Other glassy-type compounds, containing for example boron, in which elemental lithium is dissolved, have also been known to be used as anode active materials in rechargeable lithium batteries. U.S. Pat. No. 5,284,721 issued to K. W. Beard on Feb. 8, 1994, describes compounds having the general formula of Li.sub.x M.sub.a X.sub.b for utilization in the anode of a lithium secondary battery, where M is one of scandium, titanium, yttrium or zirconium, and X is a chalcogen, usually oxygen or sulphur. In particular, K. W. Beard utilizes lithium titanium oxides as anode active compounds. Koksbang et al. in U.S. Pat. No. 5,418,090, issued on May 23, 1995 describe the use of lithium-manganese compounds of different oxygen contents in the anode and in the cathode of a rechargeable lithium battery. Yoshio Idota in U.S. Pat. No. 5,478,671 describes the use of a lithium-transition metal oxide or a lithium-transition metal vanadate as the anode-active material of a rechargeable lithium battery. There are several other instances in which a metal oxide or a metalloid oxide doped with lithium is the active material of the anode of a rechargeable lithium battery, for example, in U.S. Pat. No. 5,545,468, issued on Aug. 13, 1996 to Nobuharu Koshiba et al. a rechargeable lithium battery anode is described, containing a lithium bearing titanate having the general formula Li.sub.x Ti.sub.y O.sub.4, and having a specific crystal structure. Tin oxide is also known to be capable of incorporating lithium ions and hence to form the negative-active component of the anode of a rechargeable lithium battery. It is noted, however, that the above discussed lithium-metal oxide compounds although capable of providing lithium secondary batteries having high energy density initially, often exhibit a noticeable drop in the energy density after repeated discharging and charging, suggesting that the insertion of lithium ions in the anode active component may become irreversible due to changes in crystal structure or grain size, or to similar effects. In other words, the above described oxide compounds may replace carbon as the conventional anode active material utilized in rechargeable lithium batteries, however, their readiness in incorporating lithium ions reversibly and repeatedly has not been clearly demonstrated.
There is a need for an anode active compound for use in a rechargeable lithium battery, which is oxidation and corrosion resistant, provides high reversible anode capacity even after repeated cycling and which is also dense.